Body Mass Index, but Not Age at Puberty, Linked to Higher MS Risk, Study Suggests

Body mass index (BMI), but not the age at which people start puberty, could increase the risk of multiple sclerosis (MS), a study suggests.

The study, “Effect of age at puberty on risk of multiple sclerosis: A mendelian randomization study,” was published in the journal Neurology.

Some studies have suggested that people who start puberty at an earlier age are more likely to develop MS, but a high BMI is also linked to both an earlier start to puberty and MS risk.

“Previous studies have shown that children with higher body weight tend to enter puberty earlier than children with normal body weight, and increased BMI is also linked to a greater risk of MS,” J. Brent Richards, MD, a professor at McGill University in Montreal and one of the authors of the study, said in a press release.

To try to untangle this relationship, the researchers analyzed data from a previous genome-wide association study (GWAS) — an approach used to link genetic variants to different traits. They looked at information on more than 300,000 women, and specifically assessed data on 372 genetic variants known to be linked to age at menarche (the first occurrence of menstruation).

Since the genetic factors that help control the start of puberty are similar between males and females, the researchers used these variants as a proxy for determining age at the start of puberty. This indirect method allowed the team to analyze data on a more global and objective scale, given that when someone starts puberty can be somewhat subjective. However, the fact that the method is indirect is one of the admitted weaknesses of the study.

Researchers used a similar method to identify variants linked to BMI.

Using these variants, they looked at data from another GWAS study that included 14,802 people with MS and 26,703 individuals used as controls.

Researchers did find an association between starting puberty earlier and developing MS, but once BMI was taken into account, this association disappeared. This suggests that BMI may be the cause behind both an increased risk of MS and earlier puberty onset.

It’s important to note that this study is only showing a correlation; more research is still needed to determine whether there’s a causal link.

“It appears that earlier age at puberty is associated with an increased risk of MS, but this association is influenced by BMI. Our findings do not support a substantial role for the effect of the timing of puberty on the risk of MS independent of BMI,” Richards said.

“More research is needed to determine whether decreasing rates of obesity could help to reduce the prevalence of MS. If so, this could be another important reason for public health initiatives to focus on lowering obesity rates,” he added.